Process for the preparation of organic disulphides



Patented Apr. 9, 1940 1 UNITED STATES.

PROCESS FOR THE PREPARATION OF ORGANIC DISULPHIDES Roger A. Mathes,Akron, Ohio, assignor to The. B. F. Goodrich Company, New York, N. Y., acorporation of New York No Drawing.

Application November 18, 1938,

Serial No. 241,200

9 Claims.

where R and R represent like or unlike radicals which may be hydrogenatoms, alkyl groups, aryl groups, substituted aryl groups, alkoxygroups, 1 carbalkoxy groups, phenylamino groups, ketoani-y lino groups,etc. R and R. may also be joined together to form an alicyclic ring.

The preferred method of practicing the inven- 30 tion consists insuspending a mercaptoalkylthiazole in aqueous medium and adding theretoa hypochlorite. I

Specific reaction conditions are necessary to obtain satisfactoryresults when employing my 35 process. A common procedure in theformation of an organic disulphide by the oxidation of a sulphydrylcompound is to carry the oxidation out while dissolved in an alkalinesolution. In my process, the mercaptoalkylthiazoles are preferm ablypresent as a suspension. For best results,

such a suspension is formed by dissolving the g mercapto body in analkali and precipitating by the addition of an acid, as sulphuric acid.By this procedure, the mercaptoalkylthiazole is ob- 5 tained as a veryfine suspension, and a more complete oxidation is insured than whenusing a mechanically ground powder. aqueous suspension is preferablymaintained in an alkaline condition. The yield is somewhat in- 50creased when the alkalinity is' furnished by a selected mild alkali, assodium carbonate, rather than an alkali metal hydroxide. For the samereason, the hypochlorite solution to be used in the oxidation iscarefully prepared to avoid an unnecessary excess of free alkali. In thecase of al- Furthermore, the

kali metalv hypochlorites, a small amount of free alkali is howevernecessary to insure reasonable stability. While water is usuallyemployed as a diluent for carrying out the oxidation, organic solventsmay also be used. In general, mercaptoalkylthiazoles are appreciablysoluble in organic solvents while the di(alkylthiazyl) disulphides areeven more soluble. The process is therefore somewhat more involved andin addition would require recovery of the oxidation product fromsolution as wellas recovery of the organic solvent. The oxidationproducts are not appreciably soluble in water, and the water filtrate,containing the by.-product inorganic salt formed in the reaction, isdiscarded.

The use of oxidation catalysts, as nickel and cobalt salts, is notnecessary. Hypochlorite ofiers an oxidizing agent that may be used atlow temperatures which is, in general, desirable when 0xidizingmercaptoalkylthiazoles. The oxidation products in many cases are lowmelting compounds. i

Alkali metal hypochlorites, particularly sodium hypochlorites, giveexcellent results in my process. They maybe readily prepared at a lowcost. Satisfactory results may also be obtained with many otherhypochlorites, as for example calcium hypochlorite. Esters ofhypochlorous acid, as tertiary butyl hypochlorite, may be used ifdesired. Hypobromites and hypoiodides give results similar to thoseobtained with hypochlorites but are of minor importance due to theircomparatively high cost.

Mercaptoalkylthiazoles which may be oxidized to the correspondingdisulphides by my process, include, among others, 2-mercaptothiazole;.2- mercapto 4,5-dimethyl thiazole; Z-mercapto 4- ethyl thiazole;2-mercapto 4-methyl thiazole; 2

mercapto 4-phenyl thiazole; 2-mercapto 4,5-cyclotetramethylene thiazole;Z-mercapto d-methyl 5-ethyl thiazole; 2-mercapto 4-methyl 5-carbethoxythiazole; Z-mercapto 4-tolylthiazole 2- mercapto 4-anilino thiazole.

Example 1 tered to remove a small amount of insoluble material. Whilestirring, 20% sulphuric acid is added until the slurry of precipitatedmercap-tothiazole is slightly acid. During thev acidification, 6 gal. ofwater and 40 lbs. of ice are added for the white, thick reaction mixtureto a light brown precipitate not as finely-divided.

After standing several hours the product is filtered oiT, washed anddried at room temperature. The dry weight is 21.4 lbs., representing an86.3% yield. The melting point of the di(4,5-dimethylthiazyl) disulphideis 42-46 C.

Example '2 72.5 g. of 2-mercapto 4,5-dimethylthiazole are dissolved inan alkali solution prepared by dissolving 22 g. of sodium hydroxide in500 cc. of water. Dilute hydrochloric acid is added while stirring toprecipitate the mercaptothiazole as a finely-divided suspension. Thesuspension is made alkaline by the addition of a small amount of sodiumcarbonate. The oxidizing agent is prepared by dissolving 48 g. ofbleaching powder (70% available chlorine) in 200 cc. water. Theinsoluble material is removed by filtration. The bleaching powdersolution is added to the suspension of mercaptothiazole with agitation,over a period of minutes, while maintaining a temperature range of l4-31C. After standingseveral hours,the thin slurry of light brown di(4,5-dimethyl-thiazyl) disulphide is filtered off, washed and dried. Thedryweight is 63 g. representing'an 87.5% yield. The melting point is44-47 C.

Example 3 29 g. of 2-mercapto ll-ethyl thiazole (M. P. 78-80 C.) aredissolved in 8.8 g. of sodium hydroxide and 300 cc. of water. 20%sulphuric acid is added with stirring 'to precipitate themercaptothiazole. The slightly acid suspension is brought to an alkalinecondition by the addition of a small amount of sodium bicarbonate.

While agitating the suspension, 62 cc. of a15% solution of sodiumhypochlorite are added over a period of 30 minutes, while maintaining atemperature of l520 C. After standing several hours, the precipitate ofdi(4-ethyl thiazyl) .disulphide is filtered off, washed and dried. Thedry weight is 26.2 g. representing a 91% yield. The melting point is36-39 C.

Hypochlorites are shown, in the data presented, to have several distinctadvantages in the oxidation of mercaptcalkyl thiazoles to thecorresponding di(alkylthiazyl) disulphides. Sodium hypochlorite, as wellas bleaching powder, are inexpensive materials. A nearly quantitativeconversion of mercaptothiazoles to disulphides is obtained. The processis operative at a wide temperature range making possible the isolationof low melting products as solids. The use of oxidation catalysts is notnecessary.

I claim:

1. A proc'essffor preparing a di(alkyl thiazyl) disulphide whichcomprises oxidizing the corresponding mercapto alkyl thiazole in anaqueous medium containing alkali in a quantity insufficient to dissolvethe mercapto compound, with a hypochlorite in a quantity notsubstantially in excess of the stoichiometric equivalent required toremove one hydrogen from each molecule.

filtering ofl. the product.

2. The process of claim 1 in which thehypochlorite is an alkali metalhypochlorite.

3. A process for preparing a di(alkyl thiazyl) disulphide whichcomprises suspending the corresponding mercapto alkyl thiazole in watermaintained alkaline by an alkali metal salt of a weak acid in a quantityinsuflicient to dissolve the mercapto compound, oxidizing the mercaptocompound at approximately room temperature with an alkali metalhypochlorite in a quantity not substantially in excess of thestoichiometric equivalent required to remove one hydrogen from eachmolecule, and filtering ofi the product.

4. A process for preparing di(4,5-dimethyl thiazyl) disulphide whichcomprises oxidizing 2- mercapto 4,5-dimethyl thiazole in an aqueousmedium containing alkali in a quantity insufficient to dissolve themercapto compound, with an alkali metal hypochlorite in a quantity notsubstantially in excess of the stoichiometric equivalent required toremove one hydrogen from each molecule.

5. A process for preparing di(4,5-dimethyl thiazyl) disulphide whichcomprises suspending Z-mercapto 4,5-dimethyl thiazole in Watermaintained alkaline by a sodium salt of a weak acid in a quantityinsufficient to dissolve the mercapto compound, oxidizing themercaptocompound at approximately room temperature with sodiumhypochlorite in a quantity not substantially in excess of thestoichiometric equivalent required to remove one hydrogen from eachmolecule, and filtering off the product.

6. A process for preparing di(4-ethyl thiazyl) disulphide whichcomprises oxidizing Z-mercapto l-ethyl thiazole in an aqueous mediumcontaining alkali in a quantity insufilcient to dissolve the mercaptocompound, with an alkali metal hypo chlorite in a quantity notsubstantially in excess of the stoichiometric'equivalent required toremove one hydrogen from each molecule.

7. A process for preparing di(4-ethyl thiazyl) disulphide whichcomprises suspending 2- mercapto 4-ethyl thiazole in water maintainedalkaline by a sodium salt of a weak acid in a quantity insufiicient todissolve the mercapto compound, oxidizing the mercapto compound atapproximately room temperature with sodium hypochlorite in a quantitynot substantially in excess of the stoichiometric equivalent required4-methyl thiazole in an aqueous medium containing alkali in a quantityinsuificient to dissolve the mercapto compound, with an alkali metalhypochlorite in a quantity not substantially in excess of thestoichiometric equivalent required to remove one hydrogen from eachmolecule.

9. A process for preparing di(4-methyl thiazyl) disulphide whichcomprises suspending Z-mercapto 4-methyl thiazole in water main,- tainedalkaline by a sodium salt of a weak acid in a quantity insufiicient todissolve the mercapto compound, oxidizing the mercapto compound atapproximately room temperature with sodium hypochlorite in a quantitynot substantially in excess of the stoichiometric equivalent required toremove one hydrogen from each molecule, and

ROGER A. MATHES.

